This invention relates to surgically implantable prosthetic joints and more particularly to a unique device for and a method of protecting such joints from lacerations or tearing caused by contact with the edges of adjacent bones and protect bone from fracture.
Heretofore various surgically implantable prosthetic devices have been proposed for replacing bone joints. Typically, the prosthesis includes a midsection and a pair of outwardly directed stem portions. The stem portions correspond generally to the dimensions of the intramedullary canals of the bones adjacent the joint and are implanted within the canals. Examples of such prosthetic joints may be found in Applicant's prior U.S. Pat. No. 3,462,765, issued Aug. 26, 1969 and entitled SURGICALLY IMPLANTABLE PROSTHETIC JOINT and in Applicant's prior U.S. Pat. No. 3,875,594 issued Apr. 8, 1975 and entitled SURGICALLY IMPLANTABLE PROSTHETIC JOINT HAVING LOAD DISTRIBUTING FLEXIBLE HINGE.
Prosthetic joints of the type disclosed in the aforementioned patents are fabricated from flexible elastomeric, physiologically inert material. These flexible, one-piece joints have been widely used and have improved markedly the prognosis for restruction patients. The devices illustrated in these patents have utility in replacement of finger joints in a human hand and also may be used to replace various other joints of the human body.
Clinical experience and mechanical testing programs have indicated that the flex life of these flexible implants is essentially infinite unless a laceration occurs on the surface. If a laceration or tear of the surface of a prosthesis should occur, tear propagation throughout the device will usually result. This tear propagation can and has resulted in fracture of the prosthesis after implantation. Various causes for such lacerations or tearing of the surface have been hypothesized. For example, the damage to or fracture of the prosthesis may be the result of insufficient bone resection or an irregularity of the edges of the resected bone.
Also, with certain types of patients, especially those suffering from severe rheumatoid arthritis, fractures are more prevalent. Rheumatoid arthritis produces alterations of the bone and tendon balance of the joints and further plays an important role in the mechanism of reconstructed joints. The bones of these patients may become thin and atrophied and the edges of the bones at the joint may become very sharp. Sublaxation of the joint bones results in impingement of the sharp bone edges on the midsection of the implant and subsequent lacerations or tears. An implant may exert sufficient pressure to result in fracture of the bones themselves with these patients. As a result, these patients may be denied the benefits of such corrective procedures.
A need, therefore, exists for a device for and a method of protecting the flexible elastomeric prosthetic joint from lacerations or tearing and subsequent fracture resulting from impingement on the prosthesis by sharp bone edges adjacent the joint.